MacOS Sierra doesn’t feature an option to encrypt a USB drive in Disk Utility or in Finder (at least at the time of writing). This post covers how to format a USB drive to either the JHFS+ or the new APFS filesystem and encrypt it using the Terminal and Disk Utility.
First, plug your USB drive into your computer and open the Terminal app.
Use the following command to list your disks:
Look for an entry (or entries) like
/dev/disk2 (external, physical) and make absolutely sure that you understand the difference between your system’s hard disk and the external USB drive you want to encrypt.
The “IDENTIFIER” for my USB drive, found at the top of the list, was
disk2. My system showed a subsequent entry
disk2s1 but note how this still refers to
disk2. Only the
disk2 part is required. Use whatever
diskn number corresponds to your target drive, where
n is an integer.
Only proceed if you are certain that you have correctly identified your USB drive!
The following command formats the drive to Apple’s HFS+ with Journaling format, JHFS+.
GPT is a crucial argument here to specify the GUID Partition Map option vs. the Master Boot Record option. You can replace the text inside the quoted string (“Flash Drive”) with your desired drive name:
diskutil eraseDisk JHFS+ "Flash Drive" GPT disk2
It is now possible to encrypt the drive with Finder (right-click and choose “Encrypt ‘Flash Drive'”) if you wish to simply keep the JHFS+ file system. If you wish to use the newer APFS file system, do not Encrypt the drive just yet, and read on.
Using the new APFS file system
APFS is Apple’s latest filesystem and it features good support for encryption. Before formatting your drive to APFS, be aware that older Macs (i.e. those without MacOS Sierra and up) will not support it.
To proceed with APFS, open the Disk Utility app.
With the drive formatted to JHFS+, Disk Utility will no longer grey out the “Convert to APFS” option when you right/control+click it.
Find your drive and choose “Convert to APFS”.
Once the file system has been converted to APFS you can go back to Finder, right/control+click on your drive, and choose “Encrypt ‘Flash Drive'” from the menu.
Don’t forget your passphrase 😉